The present invention relates to the field of optical fibers.
Even more precisely, the present invention relates to the field of optical fibers which include an integrated component.
The present invention applies in particular to fiber-optic devices which include an integrated Bragg grating. Within this context, the invention aims to provide a device for temperature stabilization and/or Bragg wavelength adjustment of the gratings photowrittten in the optical fibers.
A person skilled in the art knows that it is possible to considerably increase the traffic of optical-fiber networks by the technique of xe2x80x9cwavelength multiplexingxe2x80x9d. Each series of data to be transported is transmitted over one specific optical frequency, multiplying the capacity of the fiber by the number of wavelengths used.
The number of multiplexible wavelengths in a given frequency band cannot, however, be increased ad infinitum. It depends on the levels of drift and on the degrees of precision of the devices capable of inserting a wavelength into the fiber or extracting it therefrom, without disturbing the flux of the other ones.
Among devices used, some rely on Bragg gratings written into the core of the fiber.
Bragg gratings are periodic optical index structures which have the particular feature of reflecting light of a well-defined wavelength, called the Bragg wavelength of the grating. Systems based on Bragg gratings have already been of great service. However, it turns out that this reflected wavelength, which depends on the periodicity of the grating and on the parameters of propagation in the fiber, is:
an increasing function of temperature and
an increasing function of the tension applied to the fiber.
Means for limiting the temperature drift of devices using Bragg gratings are known. The means most in use at the present time are known as tabletop or semi-tabletop arrangements. A description of illustrative examples of these means will be found in documents [1] and [2].
The appended FIGS. 1 and 2 show tabletop and semi-tabletop structures according to the prior art, respectively.
Tabletop or semi-tabletop arrangements consist of a beam 20 made of a material having a low expansion coefficientxe2x80x94invar, ceramic, etc.xe2x80x94and of one or two blocks 30, 32 made of a material having a high expansion coefficient, for example aluminum. The fibers 10 which include a Bragg grating are mounted so as to be held taught between the two blocks 30, 32 in the case of a tabletop or between the block 30 and the opposite end of the beam 20 in the case of a semi-tabletop, depending on the type of arrangement. The points for fixing the fiber 10 are labeled 12 and 14.
The distance between these two points 12, 14 decreases with increasing temperature and the tension applied to the fiber decreases and tends to reduce the Bragg wavelength, whereas, since temperature induces the opposite effect, an equilibrium is established between the two phenomena.
For this type of device to be stable over time requires the Bragg grating to be definitively held in place in this arrangement by adhesive bonding or welding. Any error between the Bragg wavelength obtained and the desired wavelength then becomes uncorrectable.
Moreover a person skilled in the art knows that the optical signal propagating in a fiber is attenuated over the course of its path. After a certain distance, it then becomes necessary to reamplify it. Many of the amplifiers used are fiber amplifiers which have the drawback of amplifying the light passing through them to a degree which varies with wavelength. To equalize the output levels of the various wavelengths, a gain-equalizing filter is added to these devices.
Gain-equalizing filters based on Bragg gratings consist of a succession of gratings with slanted lines. Each of these gratings extracts from the fiber a small portion of the light in the wavelength band corresponding to it, this amounting to producing a certain absorption in this band. The distribution of these various absorptions allows the output level of the light to be evened out, independently of its wavelength.
There is one tension value to be applied to the gain-equalizing filter in order to obtain the optimum result or, formulated another way, there is a value of the overall wavelength shift to be applied to the filter in order to have the flattest possible response.
In general, certain optical functions may require the Bragg gratings to be adjusted as desired; these are thus tunable gratings.
The objective of the invention is to provide a means of adjusting the response of fiber-optic-based devices which include an integrated component.
In particular, the objective of the present invention is to provide a means of adjusting the Bragg wavelength of tabletop or semi-tabletop arrangements.
The aforementioned objectives are achieved within the context of the present invention by a fiber-optic device comprising:
an optical fiber which includes at least one integrated component,
a support having two fixing regions to which the optical fiber is fixed at the two regions lying respectively on each side of the component, characterized in that:
the support comprises, between the two fixing regions, at least one linking beam capable of bending, and in that
the device furthermore comprises means which can impose a controlled bending on the beam, suitable for adjusting the distance between the two fixing regions.